Despite significant progress in the past, for example in the development of chemotherapeutics, antibody-based therapies, tumor vaccination, and radiation therapy, there is still an urgent and unmet need for the development of novel therapeutics and therapeutic approaches for the treatment of tumors and related malignant diseases.
While gene therapy approaches have substantial promise for such treatments, and while anti-tumoral results have been observed in different gene therapy models, certain limitations, particularly in the transfer of genes of interest to the tumor cells, have hampered the further development of such approaches.
In the past, it had occasionally been observed that natural infections or vaccinations with measles virus resulted in spontaneous tumor remissions, particularly in hematological malignancies, such as leukemias, resulting in the identification of the oncolytic potential of measles virus.
Measles virus is an enveloped, single-stranded, negative-sense paramyxo-virus of the genus Morbillivirus that is causing the infectious measles disease, an infection of the respiratory system. The genome of the measles virus contains six genes encoding eight proteins: the nucleocapsid (N), phospho- (P), matrix (M), fusion (F), hemagglutinin (H) and large (L) proteins, and two accessory proteins, termed C and V. The virus enters the target cells via pH-independent membrane fusion. The H and F proteins are involved in receptor binding and membrane fusion, respectively. Entry of measles virus into cells occurs via interaction of the surface H glycoprotein with the two known receptors for measles virus: CD46, which is ubiquitously present on nucleated primate cells, but is frequently over-expressed in tumors, and the signaling lymphocyte-activation molecule (SLAM) that is primarily located on B- and T-cells. CD46 is a membrane-associated complement regulatory protein that protects human cells against autologous complement lysis by acting as a cofactor in the proteolytic inactivation of C3b and C4b complement products, thus providing protection for tumor cells against complement-mediated lysis. Receptor recognition by the H protein leads to conformational changes of the F protein resulting in fusion with target cell membranes and subsequent viral entry. Infected cells, including tumor cells, express the viral F and H proteins on the cell surface. Recognition of the viral receptor in neighboring infected or uninfected cells similarly triggers cell-to-cell fusion. Therefore, the typical cytopathic effect of measles virus is the formation of giant mononuclear cell aggregates (syncytia).
Most of the measles virus preparations used for measles vaccines or for the research on oncolytic measles virus are based on an attenuated live measles virus derived from the so-called Edmonston vaccine strain, an isolate originally obtained in 1954, which was used to create the Edmonston-Enders cell line, and based on that, Edmonston A and B seed lines by serial passages on human cells and subsequent adaptation to chicken embryo fibroblastic (CEF) cells. Use of the originally developed live attenuated vaccine based on the Edmonston B lineage had to be stopped due to its high reactogenicity. By further attenuation of the Edmonston lines Edmonston-Enders and Edmonston A and B, additional measles derivatives were developed (Edmonston-Enders: AIK-C, Edmonston Zagreb; Edmonston A: Schwarz; Edmonston B: Moraten).
Despite the progress that has been made since the discovery of the oncolytic potential of measles virus, which is summarized in a recent review article (Msaouel, P., Dispenzieri, A., and Galanis, E., Clinical testing of engineered oncolytic measles virus strains in the treatment of cancer: An overview, Curr Opin Mol Ther. 2009; 11: 43-53), no therapeutic product based on oncolytic measles virus has yet reached the market, a fact that may, at least in part, be due to the potential of wild-type viruses to cause serious side effects, and particularly technical limitations in manufacturing virus preparations of high purity for clinical use. While the expanding knowledge of the biology of measles virus, as well as the development of a reverse genetics system that allows rescue of recombinant measles virus strains and viral engineering, have opened new opportunities for the development of measles virus as therapeutic in cancer treatment, there are still several limitations in the constructs that are presently in use.
For example, many of the research and development programs that are currently being pursued are based on the work of Martin Billeter and colleagues (Radecke, F., Spielhofer, P., Schneider, H., Kaelin, K., Huber, M., Dötsch, K, Christiansen, G., and Billeter, M., Rescue of measles viruses from cloned DNA. EMBO Journal 14 (1995) 5773-5784; WO 97/06270). Subsequently, it was shown that the sequence of the cloned viral genome deviated from the Edmonston B sequence, being closer to the wild-type Edmonston strain and having substitutions being related to the Edmonston subgroup (Parks et al., J. Virol. 75 (2001) 910-920; Parks et al., J. Virol. 75 (2001) 921-933).
Furthermore, measles virus preparations are currently rescued from cell lines not being approved for vaccine production like chicken embryo fibroblastic (CEF) cells or 293 human embryonic kidney cells, both complicating and thereby increasing the costs for the large-scale production of recombinant measles virus particles in conformity with GMP requirements.
Additionally, it has been shown that, for example, tumors derived from certain cell lines (eg, RPMI 8226 and HT1080) were resistant to treatment with oncolytic measles virus despite repeated virus injections (Peng K W, Facteau S, Wegman T, O'Kane D, Russell S J. Non-invasive in vivo monitoring of trackable viruses expressing soluble marker peptides. Nat Med. (2002); 8:527-31).
Therefore, there remains a continuous need for an improved pharmaceutical composition comprising a recombinant measles virus for use in the treatment of a malignant cells and improved methods for the generation of such pharmaceutical compositions and recombinant measles virus.